1. Field of the Invention
The present invention relates to a voice decoder, a voice decoding method and a program for decoding voice signals.
2. Description of the Related Art
Wire telephones and cellular phones send encoded voice signals (in a bit stream), converts (decodes) and outputs any of those bit streams which have been transmitted from another terminal device, etc.
Conventionally, most techniques for encoding/decoding voices signals are developed for encoding/decoding narrow band voices signals. In recent years, however, methods for encoding/decoding both narrow and wide band voice signals, such as the multi-path excitation mode of MPEG-4/CELP (Moving Picture Experts Group-4/Code Excited Linear Prediction), have been being spread.
Generally, each apparatus for encoding/decoding both the narrow and wide band voice signals is formed as follows: An apparatus specialized for handing narrow band voice signals is formed with a module specialized or optimized for handling narrow band voice signals. Then, an appropriate change is made in this apparatus, thereby forming an apparatus which can handle both narrow and wide band voice signals. The formed apparatus mainly includes the above module optimized for handling narrow band voice signals.
It should be noted, however, that the calculation accuracy of the module specialized for encoding/decoding the narrow band may not be sufficient for handling the wide band voice signal, in the case of fixed-point representation. Hence, if the wide band voice signals are decoded using the module for narrow band voice signals, only low quality of voices reproduced using decoded wide band voice signals may be obtained.
Further, in the case where an apparatus handling both the narrow and wide band voice signals is formed with a module having a sufficient level of calculation accuracy for handling wide band voice signals, unnecessary calculations may be processed when handling narrow band voice signals. This results in lowering the processing speed of the apparatus.